The present invention relates to a multi-part drawer slide, and more particularly to a sequential drawer slide wherein movement of the slide parts is sequenced during opening and closing of the drawer.
A wide variety of multi-part drawer slides has been developed to support a drawer within a cabinet. Multi-part slides permit the supported drawer to be fully withdrawn from the cabinet and are therefore often used for office filing cabinet drawers and other applications where full access to the drawer is important.
Typically, multi-part slides include a drawer slide member to be secured to a drawer, a cabinet slide member to be secured to a cabinet, and an intermediate slide member slidingly interfitted with both of the drawer and cabinet slide members. Proper coordination of the movement of the slide members is important to prevent binding and/or racking of the slide, which creates highly detrimental dynamic stress loading in the slide members. Random or uncoordinated movement of the various slide members results in (1) lateral swaying of the drawer, (2) undesirably high opening and closing forces, and (3) increased wear and decreased service life because of the dynamic stress loading.
In efforts to overcome the problems associated with random slide movement, coordinating mechanisms for multi-part slides have been developed. Such mechanisms fall into one of two broad categories--progressive slides and sequential slides. Both types of mechanisms are typically incorporated into "precision drawer slides" which have exact tolerances between the various slide components.
In progressive slides, the intermediate slide moves at exactly one-half the rate or distance of the drawer slide during all opening and closing movement. Stated another way, the intermediate slide always moves an equal distance relative both the drawer and cabinet slides. These slides most typically include rollers, cables or racks-and-pinions as the sequencing mechanism. Rollers are most frequently used; and illustrative constructions are shown in U.S. Pat. Nos. 4,067,632, issued Jan. 10, 1978 to Sekerich, entitled DRAWER SLIDE; 3,901,565, issued Aug. 26, 1975, to Hagen et al, entitled ADAPTOR AND LATCHING MEANS FOR REMOVABLY ATTACHING DRAWERS TO TELESCOPING BALL BEARING DRAWER SLIDES; and 3,901,564, issued Aug. 26, 1975, to Armstrong entitled DRAWER EXTENSIBLE SLIDE CHASSIS. However, all progressive slides have a relatively short useful life because of the relatively high and constant dynamic stresses borne primarily by the cabinet slide member as the intermediate slide member always moves relative thereto. Further, all progressive coordinating mechanisms create a constant resistive opening and closing force or drag. Those mechanisms utilizing a roller also wear rapidly with subsequent failure. All of these problems are exacerbated when the drawers are wide and/or heavily loaded--for example in one of the most common uses in lateral file cabinets.
Sequential drawer slides were developed in part to enhance the life of the drawer slide by reducing the dynamic stress loading on all of the slide members, particularly the cabinet member. In sequential slides, only two slide members are permitted to move relative one another at any given time. Movement of the drawer slide member with respect to the intermediate slide member occurs only when the intermediate slide member is locked with respect to the cabinet slide member and vice versa. Most desirably, the sequencing mechanism (1) interlocks the drawer and intermediate slide members during their extension as the drawer is initially withdrawn from the cabinet, and then (2) releases the drawer and intermediate members and interlocks the fully extended intermediate slide member and the cabinet slide member as the drawer slide member is extended as opening is continued. The sequencing mechanism insures full extension of the intermediate slide member before any extension of the drawer slide member to reduce the dynamic stress loading on the cabinet slide member and enhance the life of the slide. However, known sequencing mechanisms often "catch" and require a large opening or closing force at the transition point between movement of the intermediate slide member and the drawer slide member. Further, known sequencing mechanisms are relatively complex, resulting in high manufacturing cost and less than desirable reliability.